1. Field of the Invention
This invention relates to cleaning compositions for cleaning printing inks, and the like, from printing rollers, blankets, machinery, and the like. More particularly, this invention relates to cleaning compositions that combine, inter alia., good solvency power in printing inks with low volatility of potentially hazardous organic compounds.
2. Background of the Invention
Offset printing, also known as offset lithography, is a large and established industry which encompasses from the newspaper industry to quick copy shops. In the United States alone, over 60,000 plants and businesses are dedicated to offset printing.
Offset printing can be performed on a wide variety of printing press equipment, including sheet-fed and web systems. These printing systems are available in a wide variety of sizes and speeds. A common factor of the above offset printing systems is the method of offset printing, i.e., printing ink which is typically manufactured from various petroleum or vegetable oil sources, is applied to a substrate such as paper, plastic, or foil. The printing ink is applied by way of ink rollers to a printing plate which transfers the printed image to the impression cylinder which is covered with a rubber printing blanket. The printing blanket then transfers the printed image to the substrate.
Periodically, the ink rollers and printing blankets need to be cleaned to insure the quality of the printing or to change ink colors for another printing job. It is known that offset printers are routinely contacted with many solvents and compounds which are used for cleaning the printing ink therefrom. The most commonly used solvents are generically classified as aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons and oxygenated solvents. Aliphatic hydrocarbons are characterized by a straight or branch chain arrangement of constituent carbon atoms. The aliphatic hydrocarbons are comprised of three subgroups: (1) paraffins, (2) olefins, and (3) acetylenes. Aromatic hydrocarbons are characterized by unsaturated cyclic hydrocarbons containing one or more rings. They are typified by a benzene adduct which comprises a six-carbon ring containing three double bonds. Chlorinated hydrocarbons comprise carbon chain in which one or more of the hydrogen atoms has been replaced by chlorine. Oxygenated solvents are those having hydroxyl or carbonyl groups which are more polar that the relatively nonpolar hydrocarbon solvents.
However, organic solvents used for cleaning inks create environmental and physiological problems in industry. Volatile organic compounds emitted therefrom are known to be hazardous. It would be desirable to provide a cleaning composition for printing inks and the like having low volatility of organic compounds combined with good solvency power. In the past, printers used the above types of solvents and combinations thereof without regard to emissions and pollution concerns. Furthermore, many solvent products used to clean printing inks contained carcinogenic or reproductive toxins, thereby exposing workers to unnecessary risks.
The heightened awareness of the hazardous nature of the above solvent compositions has led legislators to promulgate new and more stringent air pollution and safety laws. Therefore alternative technologies used for cleaning printing ink from rollers and blankets are now being requested by the marketplace. More specifically, the new Clean Air Act of 1990 has placed tremendous pressures on printers to reduce their emissions, otherwise known as volatile organic compounds (VOC's).
The current conventional cleaning composition technologies are petroleum solvents, chlorinated hydrocarbons, and other organic chemicals which approach 100% VOC content. The Clean Air Act and various state laws, such as California Rule 1172, require printers to acquire emission permits to limit and reduce the use of VOC products in their operations. Thus it would be desirable to provide alternative cleaning compositions to lower VOC's without sacrificing cleaning efficiency and productivity. Furthermore, the reduction of VOC's relates to increased worker safety, since reduced VOC's translates to less solvent exposure to the user.
Various alternative technologies to reduce VOC's have been developed and marketed with limited success. U.S. Pat. No. 5,104,567 discloses environmentally acceptable cleaning liquids for the removal of printing inks consisting of 90-99% vegetable oil, in particular soy oil, and 1-10% surfactant emulsifier. These compositions were specifically designed to replace traditional cleaning liquids based on petroleum spirit and other mineral oil products and aromatic solvents. However, although this technology reduces VOC's, it requires constant rinsing with water, contributing to hazardous waste generation, to remove the oily residue which remains on the roller and blanket surfaces. Also, if the emulsifier is not completely removed from the ink rollers, the ink will not adhere to the rollers and "stripping" will occur. This type of roller contamination is common when using products with such a high emulsifier content. Furthermore, these types of products lack sufficient cleaning power or cutting ability to clean ink efficiently which increases production downtime.
Another technology known to lower the VOC's of printing ink cleaners includes blending organic solvents with water and emulsifiers. In this technology, the water acts as a zero VOC base of the product. Unfortunately, water does not clean, i.e., solubilize or degrade, printing ink (i.e., oil based) and weakens the performance of the cleaner, thereby decreasing cleaning efficiency and productivity. These products also tend to be unstable emulsions which separate in storage containers and easily freeze in transportation.
In an attempt to stabilize such an emulsion, U.S. Pat. No. 4,511,488 discloses an emulsion cleaning agent based on D'limonene, a terpene hydrocarbon. This water/terpene/emulsifier blend effectively lowers VOC's, but because so much emulsifier is used to stabilize the product, roller contamination again becomes a production concern. Additionally, water technologies cannot be used in cleaning inks from webs presses while they are at full production speed which is a common occurrence. This is due to the fact that water will tear the substrate, such as paper, and "break" the web, thereby, resulting in press downtime.
Other attempts to reduce VOC's from ink cleaning compositions using non-aqueous bio-degradable liquid compositions are known. U.S. Pat. No. 4,664,721 discloses a printing ink cleaning composition consisting essentially of about 30-85% N-methyl-2-pryyolidone, about 10-35% of an oxygenated solvent and about 1-5% of a surfactant. However, these products are 80-90% volatile by volume.
Tall oil fatty acid esters are known in the printing ink industry as a component of printing inks themselves, which are employed to reduce tack and viscosity of ink compositions. However it has not heretofore been suggested that such aliphatic esters, such as tall oil fatty acid esters, may be used in combination with other solvents and surfactants as an ink cleaning composition with low VOC content and good solvency power to be effective and also comply with environmental health and safety standards.
In addition, other cleaning compositions that contain tall oils, tall oil fatty acids and derivatives of tall oil fatty acids are disclosed in U.S. Pat. Nos. 3,923,701; 4,673,524; 4,822,514; 5,041,235; and 5,103,730.